Reflections of Consciousness: The Mirror Test Pentti O A Haikonen Nokia Research Center P.O. Box 407 FI-00045 NOKIA GROUP Finland [email protected] Abstract of the hand motion command and the visually detected Humans and some animals are able to recognize motion of the mirror image (Michel, Gold and Scassellati themselves in a mirror. This ability has been taken as a 2004, Gold and Scassellati 2005, 2006). Fitzpatrick, demonstration of self-consciousness. Consequently, it has Arsenio and Torres-Jara at MIT have implemented similar been proposed that the self-recognition in the mirror image, binding between the proprioceptive information and visual the mirror test, could also be used to determine the potential mirror image information of robot hand movement in the self-consciousness of cognitive machines. Cog robot for the purpose of mirror image self-recognition It is shown that very simple machinery is able to pass the (Fitzpatrick and Arsenio 2004, Fitzpatrick, Arsenio and mirror test and consequently it is argued that the passing of Torres-Jara 2004). Superficially these robots might seem to the mirror test per se does not demonstrate the existence of be more self-aware than most animals; however, the self-consciousness. Next, the realization of more complex machinery that passes the mirror test and could be situation may be more complex than that. Self-awareness considered to possess self-consciousness is outlined. and mirror image recognition may go together, but the lack of the latter may not necessarily prove the lack of the former. (Are cats definitely without any kind of self- Introduction awareness?) Also, the presence of the latter may not necessarily be a proof of the former as will be shown in the Humans and some animals recognize their mirror image following. while other animals may treat their mirror image as another animal behind the mirror. Human babies under 18 months of age do not normally recognize their mirror image. Mirror Image Recognition Mechanisms Psychological tests have shown that babies seem to become socially self-aware around the time when they How does one learn to recognize one’s own face in a begin to recognize themselves in a mirror (Lewis et al mirror? Obviously no visual pattern matching can be done, 1989). This observation would seem to link self-awareness as initially one does not have any visual reference image of and mirror image recognition together. Consequently, one’s appearance. Therefore the mirror image self- mirror image recognition, especially the so-called rouge recognition cannot be based on specific features within the test, has been used in developmental psychology to visual modality only. However, one may utilize certain determine the time of the emergence of self-awareness in strategies that may lead to the mirror image self- very young children. In the seventies Gordon Gallup recognition. applied the mirror test to chimpanzees, who passed the test Firstly, there are body parts that can be seen directly and (Gallup 1970). Most other animals including cats and dogs this visual information may be compared to the mirror do not pass this test as many of us may have personally image of the same parts. In this way, by the common visual noticed. features and common motion the correspondence and It has been proposed that the mirror test could also be causal connection between the body part and its mirror applied to potentially conscious machines; if the machine image may be discovered. Thus, for instance, the mirror is able to recognize itself in the mirror then the machine image of a hand may be taken to represent the real hand, should be self-aware. Junichi Takeno of Meiji University, even though this conclusion is not necessarily inevitable. Japan, has built small robots that demonstrate different This outcome would allow the idea of a mirror; things seen inner activity when confronted by their mirror image and in a mirror represent real objects that are outside the another similar looking robot. Takeno proposes that this is mirror. Thus, when one’s hand touches the face, the mirror a demonstration of the robot’s self-awareness (Takeno, image of the hand is known to represent one’s own hand Inaba and Suzuki 2005). Michel, Gold and Scassellati of and consequently the mirror image of the face may also be Yale University have programmed their robot “Nico” to taken to represent one’s own face and not something that is recognize the mirror image of its hand by the simultaneity behind the mirror. 67 Secondly, facial mirror image self-recognition may arise the mirror image of its own blinking led. (In practice some from the utilization of amodal features that are related to kind of temporal filtering would be required to filter out facial expressions. Amodal features are features that are transient random correlations.) shared by several sensory modalities and manifest This kind of circuitry, perhaps with infrared diodes that themselves simultaneously. Facial expressions are conceal the true nature of operation, could be easily built generated by the commanding of certain facial muscles. into a doll. The output of this circuit might be used to The activity of these muscles lead to the excitation of trigger suitable hand motions and perhaps stored voice cutaneous receptors in the skin, which in turn leads to messages like “It’s me”, whenever the doll were positioned corresponding somatosensory sensations. The timing of the in front of a mirror. To an external observer the doll would somatosensory sensation patterns corresponds to the seem to be able to recognize itself in the mirror. In reality perceived timing of the visual change in the mirror image though, this doll would not be conscious at all. and is in this case the amodal feature that can be utilized. The circuit of Figure 1 is a most trivial one, but it should On the other hand the somatosensory sensations relate to be obvious that the principle would apply also to more the bodily self and the coincident changes in the mirror complicated situations. Instead of a solitary LED there image may lead to the association of the somatosensory could be an array of LEDs depicting a face. Or, there could bodily self with the mirror image. In the following this be an artificial face that could display various expressions approach is elaborated. effected by corresponding motor commands. The self- image detection principle of Figure 1 would still work, as the detection process is based on amodal properties: the Trivial Passing of the Mirror Test timing and temporal pattern of the motor commands and the received visual changes. It is also obvious that various The principle of the utilization of amodal features in artificial neural network schemes could be used to execute mirror image self-recognition can be easily demonstrated the correlation AND function. by trivial electronic circuits. As an example a simple case This example should show that it is easy to build is considered. In this example the “face” of the robot machines that “recognize” themselves in a mirror. contains one blinking light emitting diode LED for “facial However, the author argues that this kind of recognition is expressions” and one photodiode as an “eye”. If the not true self-recognition because these machines do not reflected light from the system’s own “facial” LED and the have an inner concept of self or a general “self-model” or a light from a similar external blinking LED cause different “sense of self”, which, for instance, Holland and Goodman output states then the system can be said to pass the mirror (2003) and Kawamura et al (2005) find necessary. These test, see Figure 1. machines would not possess any concept of self that could be evoked by the “self-image detected” signal. Therefore photo- mirror diode R this kind of passing of the mirror test is trivial and does not detector AND have much to do with consciousness. S "self- LED pulse T Somatosensory Grounding of Self-Concepts image generator detected" Humans and robots have bodies that remain the same when the environment changes. Wherever I go, my body Figure 1. A trivial circuit that “passes” the mirror test goes, too, and the sensations of my body follow me while the percepts of environment change. Therefore the concept In Figure 1 a pulse generator supplies a train of digital “I” is naturally associated with the body. The brain, electric pulses T to the “facial” light emitting diode LED however, cannot associate concepts and objects with each causing it to blink. The blinking light from that LED is other directly, only internal representations of these can be reflected via a mirror to the “eye”, a photodiode. The associated. Thus, for example, Damasio (2000, p. 22) has photodiode receives the blinking light and the detector proposed that at the basic level the sense of self is circuit generates the corresponding train of received digital grounded to the representations (percepts) of the body. pulses R. If these pulses are caused by the blinking light This view is shared by the author. from the “facial” LED then the signals R and T correspond The boundary of the body is the skin, which is saturated to each other and appear simultaneously. This correlation with various receptors for touch, temperature and pain can be detected by the logical AND function: S = R AND (cutaneous sensations). Touch information is provided by T. If S = 1 then the mirror image of the self-generated light mechanoreceptors that are sensitive to local pressure, pulse is detected. If, on the other hand, the photodiode does vibration and stretching. The position and motion of the not receive any light pulses or receives light pulses from limbs are sensed by stretch receptors in the muscles and some external sources then no correspondence between the joints (kinesthetic sensing).